Bacteroides species are some of the most common bacteria in the human gut.

Enviornmental Health Perspectives

There's no magic elixir for healthy aging, but here's one more thing to add to the list: good gut health.

A study published in the latest issue of Nature finds diet may be key to promoting diverse communities of beneficial bacteria in the guts of older people.

To evaluate this, researchers analyzed the microbiota, or gut bacteria, of 178 older folks, mostly in their 70s and 80s.

Some of the people were living in their own homes, and their diets were rich in fiber, fruits, vegetables, grains, poultry and fish.

Others were living in long-term care facilities or nursing homes where the typical diet was much less varied. "Mashed potato and porridge were the only staples in this diet type that were consumed daily," explains Paul O'Toole of the Alimentary Pharmabiotic Centre at University College Cork in Ireland. Meals were supplemented with puddings, cookies and sugar-sweetened beverages such as tea.

O'Toole's team found that people living independently, who had the most diverse diets, also had more varied gut bacteria. Andthey also scored better on clinical tests measuring frailty and cognitive function. In other words, "they were healthier older people," says O'Toole.

There may be many factors at play here, but O'Toole thinks diet is key. "We were surprised that the correlations between microbiota and health came out so strongly," O'Toole says.

There's an explosion of research into the gut microbiome as scientists fine-tune methods to analyze bacteria in the gut, and with that comes an emerging body of evidence that diversity of gut bacteria is important.

"What we're only now beginning to realize is that there's very close interaction between the bacteria within GI tract and human health and disease," says Ilseung Cho, a gastroenterologist at NYU School of Medicine.

Beneficial bacteria do a lot for us, says Cho. They help with digestion, help our bodies make vitamins, and also likely help support a strong immune system.

But they also have to compete with the harmful bacteria. That's why we want a variety of the good kind in our guts.

"If you have a lot of diversity and one bacteria that's doing something good is knocked out," explains Cho, "then you may have other bacteria that can compensate for that loss."

These new findings are not proof that diverse microbiota lead to better health. But experts say this paper is important because it establishes a link.

"Is it really that diet is altering the health of individuals through altering the gut microbiota?" asks Gary Wu of the University of Pennsylvania. "Or is it that people who are not as well tend to be housed in long-term care facilities?" It's possible that the lack of bacterial diversity isn't the cause of illness, but a sign of sickness.

Wu says it will take additional studies to unravel cause and effect. Nonetheless, he says, this new Nature paper is intriguing.

"I think there's growing evidence that diet is very important in regulating the composition of the gut microbes," says Wu.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

RENEE MONTAGNE, HOST:

There's no magic elixir for healthy aging, but there's one more thing to add to the list: good gut health. There's been an explosion of research lately with scientists learning more about the importance of beneficial bacteria that thrive in the digestive tract. As NPR's Allison Aubrey reports, a new study of older people finds eating a diet that helps maintain a diversity of bacteria is linked to better health.

ALLISON AUBREY, BYLINE: If you think about the human gut as a factory, the food we eat is sort of like the raw material. It helps determine what kinds of bacteria can thrive. And Professor Ilseung Cho of NYU School of Medicine says the more diverse the bacteria is in our guts, the better.

ILSEUNG CHO: So the idea of diversity in a bacterial community, or in the gut microbiome, is actually fairly important. And what we're only now beginning to realize is that there is a very close interaction between the bacteria within the GI tract and human health and disease.

AUBREY: He says beneficial bacteria do a lot for us. They help with digestion, help our bodies make vitamins, but they also have to compete with the harmful bacteria. That's why we want a variety of the good kind.

CHO: So if you have a lot of diversity and one bacteria that's doing something that's good is knocked out, then you might have other bacteria that can compensate for that loss.

AUBREY: Now, to get a handle on who might have diverse communities of gut bacteria, researchers at the University College Cork in Ireland decided to study a group of older folks. Some were living in nursing homes or assisted living. Others lived in their own homes. And lead author Paul O'Toole says what he found were big differences.

PAUL O'TOOLE: We were startled to be confronted with the observation that the kind of microbiota in your intestines depends on where you live.

AUBREY: If you lived at home, O'Toole says, you tended to have a rich diversity of bacteria. But those living in long-term care facilities had, by comparison, fairly impoverished communities of gut bacteria. Now, there may be many factors at play here, but O'Toole thinks one is key.

O'TOOLE: Well, what explains it is the diet, because uniquely, we're one of the few microbiota studies which has all this clinical data and also dietary habits.

AUBREY: O'Toole explains, at home, the seniors had fairly high-fiber diets. They ate fruits, vegetables, lean meats and fish. Their meals tended to vary and include a range of grains and proteins. By comparison, the diet in nursing homes had much less variety.

O'TOOLE: Mashed potato and porridge were the only staples in the diet type that were consumed daily.

AUBREY: There was also lots of sweetened tea, puddings and biscuits or cookies. O'Toole says that when you put this whole picture together, he saw that the people with the diverse microbiota also scored better on clinical tests gauging mobility, cognition and overall health, and the results were stronger than he expected.

O'TOOLE: I think we were surprised that the correlations between microbiota and health came out so strongly.

AUBREY: These findings, which are published in the journal Nature, are not proof that diverse microbiota are leading to better health. Physician Gary Wu of the University of Pennsylvania says as important and intriguing as this paper is, it establishes a link, not a cause.

GARY WU: Is it really that diet is altering the health of the individual through altering the gut microbiota? Or is it that people who are just not as well tend to be housed in long-term care facilities?

AUBREY: And their unhealthy guts are just another indicator of sickness. Wu says unraveling the cause and effect is what researchers will try to do in future studies. Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.